1. Field of the Invention
The invention generally relates to navigation of mobile devices. In particular, the invention relates to localization and mapping techniques that can be used in vehicles, such as in mobile robots.
2. Description of the Related Art
Mobile robots are becoming more and more commonplace in society. It will be understood that these robots can be embodied in a variety of forms, such as in automated vacuum cleaners. A variety of applications can be found for mobile robots, such as, but not limited to, entertainment applications, such as toy robots, utility applications in environments that are unfriendly to humans, such as space, deep water, cold temperature, radiation, chemical exposure, biohazards, etc., dangerous tasks such as defusing of potential explosives, operation in confined spaces, such as collapsed buildings, the performance of menial tasks, such as cleaning, etc. Conventional robots that are mobile do not include automated localization and/or mapping functionality.
Localization techniques refer to processes by which a robot determines its position with respect to its surroundings. For example, in a “pure” localization system, the robot is provided with a map of its surroundings. Such “pure” localization systems are disadvantageous because generating a map via manual techniques is a relatively difficult, labor-intensive, and specialized task. Moreover, many environments are not static. For example, the rearranging of furniture in a room can render a preexisting map unusable. As a result, maps in pure localization systems are subject to relatively frequent and costly updates such that the map accurately represents its surroundings.
Mapping techniques relate to processes by which a robot builds a map of its surroundings. A robot that can autonomously build a map of its surroundings and can localize itself within the map can advantageously exhibit a relatively high degree of autonomy. Moreover, such a robot can advantageously adapt to changes in its surroundings. This process of building a map and using the generated map is known as Simultaneous Localization and Mapping (SLAM). It will be understood that while SLAM relates to the building of a map (mapping) and the use of the map (localizing), a process associated with localization and a process associated with mapping need not actually be performed simultaneously for a system to perform SLAM. For example, procedures can be performed in a multiplexed fashion. Rather, it is sufficient that a system is capable of both localization and mapping in order to perform SLAM. For example, a SLAM system can use the same data to both localize a vehicle, such as a mobile robot, within a map and also to update the map.
SLAM processes typically use probabilistic techniques, such as Bayesian Estimation. Various states of a dynamic system, such as various hypotheses of a location of a robot and/or a map of robot, can be simultaneously maintained. With probabilistic techniques, a probability density function represents the distribution of probability over these various states of the system. The probability density function can be approximated with a finite number of sample points, termed “particles.”
Conventional SLAM techniques exhibit relatively many disadvantages. For example, one conventional SLAM technique builds a map using a laser rangefinder. Such laser rangefinder techniques, while accurate, are relatively unreliable in dynamic environments such as environments where people are walking. In addition, a laser rangefinder is a relatively expensive instrument, and can be cost prohibitive for many robot applications.
One conventional SLAM technique uses an Expectation Maximization (EM) algorithm to generate a map. Disadvantageously, such EM techniques are computationally intensive and are difficult to compute in real time.
One conventional technique for localization uses visual images taken from a 3-camera array. Disadvantageously, low-production volume multiple cameras cost substantially more than mass-produced single cameras. Moreover, conventional techniques utilizing visual images are not capable of autonomous mapping.